1. Field of the Invention
The present invention relates to an electrical heating apparatus provided with a positive temperature coefficient (PTC) element which generates heat upon energization thereof (i.e., by passing electric current through the element). This element is herein referred to as an “energization heat-generating element” or “electro-heat-generating element.” The invention also relates to a method of manufacturing a heat generator unit as well as to a pressing jig for use in the method of manufacturing the heat generator unit.
2. Description of the Related Art
There is known in, e.g., JP-A-5-169967, an electrical heating apparatus comprising a PTC element which generates heat upon energization thereof, and a plurality of laminated fins for radiating the heat of the PTC element.
As this kind of electrical heating apparatus, there is one in which an electrode plate and an insulating plate are sequentially laminated on an electro-heat-generating element, and the semi-product thus obtained is housed into an electrically conductive tube. The tube is then adhered, on an outside surface thereof, to fins by pressure welding or adhesion. This kind of electrical heating apparatus can generate heat as a result of energization (i.e., supplying of electricity) by connecting the electrode plate and the fins or tube to a positive pole and a negative pole, respectively, of the power source.
This kind of conventional art has the following problems. An electro-heat-generating element such as a PTC element, can neither smoothly generate nor radiate heat when the contact pressure relative to the electrode plate and to the tube is lower than a set pressure, resulting in a problem in that a sufficient amount of heat generation cannot be attained. In other words, when the contact pressure between the electro-heat-generating element and the tube is low, the heat generated in the electro-heat-generating element is not smoothly transmitted to the tube. In this case, the temperature of the electro-heat-generating element itself becomes high, and the value of resistance becomes high and, consequently, the energization and heat generation cannot be smoothly performed.
If the apparatus is provided with an urging member such as a spring for securing a contact pressure between the electro-heat-generating element and the tube, the number of constituent parts increases and the cost and weight increase.
On the other hand, it is also possible to fabricate the tube by pressing in order to secure a contact pressure between the electro-heat-generating element and the tube. In this case, it is difficult to press the tube (i.e., to fabricate the tube by press working) so as not to subject the tube to an excessive load in order to prevent the electro-heat-generating element housed therein from getting damaged. In addition, in case both end portions are pressed so as not to pressurize the electro-heat-generating element, the upper wall and the lower wall of the tube will be deformed in a manner to swell outside, resulting in incapability of obtaining the desired contact pressure.
Still furthermore, if the tube is pressed, the fins cannot be brazed to the tube in a step prior to the step of pressing. In addition, if the fins are brazed after the electro-heat-generating element has been inserted, the heat of brazing will damage the electro-heat-generating element.
Therefore, the fins will have to be brought into contact with, or adhered to, the tube without brazing. However, if the fins and the tube are brought into contact with, or adhered to, each other, the product thus obtained will be inferior in characteristics of heat transfer from the tube to the fins, as compared with a brazed one, resulting in lowering in the heat generating capacity.
As noted above, it has conventionally been difficult to: secure a contact pressure between the tube and the electro-heat-generating element without using an urging member; and to secure heat transfer performance from the tube to the fins to attain sufficient heat generating performance of the electro-heat-generating element.